Manholes and Manhole Covers: EN 124 Load Classes, Chambers and HDPE Manholes

Quick Answer

A manhole is a chamber with a removable cover on a drain or sewer that permits entry by personnel; an inspection chamber admits cleaning and inspection equipment but not people (EN 476). Where no national rules apply, EN 476 sets a minimum internal size for a manhole of 1,000 mm diameter (800 mm only in exceptional cases) and a cover clear opening of at least 600 mm. Chambers are made of precast concrete (EN 1917), masonry or plastics: PE, PP and PVC-U chambers for traffic areas fall under EN 13598-2, whose 2016 scope reaches 6 m to invert. Covers and frames are made to EN 124-1:2015 plus a material part. Its six classes are named by test load in kN: A15 (pedestrians and cyclists), B125 (footways, car parks), C250 (gully tops in the kerbside channel zone), D400 (carriageways, hard shoulders, parking for all vehicles), E600 (high wheel loads such as docks) and F900 (aircraft pavements). The class is chosen by installation location, not by vehicle weight. Round covers cannot fall through their own opening; square ones can, along the diagonal. HDPE chambers need a buoyancy check against groundwater and a concrete ring that carries traffic loads past the plastic shaft.

A typical enquiry reads: "20 manholes with covers, C250, for a new access road." The covers will sit in the running lanes, and under EN 124 a manhole top in a carriageway needs class D400 at least; C250 is for gully tops in the kerbside channel. The "25 tonnes" quoted for C250 makes it sound adequate for lorries, but it is a laboratory test load, not a vehicle rating.

The chambers raise their own questions. A DN600 "manhole" is too small to enter under EN 476, and a light plastic chamber will float if groundwater returns before backfilling is finished. This guide covers chambers, covers and the checks that prevent these mistakes.

Manhole or inspection chamber?

EN 476 gives the definitions:

• Manhole: a chamber with a removable cover, constructed on a drain or sewer to permit entry by personnel
• Inspection chamber: a chamber with a removable cover that permits cleaning and inspection equipment to be introduced from the surface, but does not provide access for personnel

EN 476 is a general-requirements standard. Product standards must respect it, but products are not assessed against it directly, so ask which product standard a chamber or cover is made to.

Inspection chamber sizes vary by country. By these definitions a DN600 chamber is an inspection chamber, not a man-entry manhole.

A manhole is built up from a base with benching and channels, chamber and shaft sections, a cone or reducing slab, adjustment units and the frame and cover. Entry is by steps (EN 13101) or fixed ladders (EN 14396), and it is confined-space work.

Chamber materials

The 2016 edition of EN 13598-2 covers plastic manholes and inspection chambers in pedestrian or vehicular traffic areas to a maximum depth of 6 m from ground level to the invert. Shallow non-road inspection chambers down to 1.25 m fall under EN 13598-1. Frames, covers and gratings are specified to EN 124.

Why corrosion drives the choice in sewers. Where sewage turns septic, typically downstream of long rising mains, bacteria produce hydrogen sulfide. Turbulence at drops releases it, and bacteria on the moist walls above the flow oxidise it to sulfuric acid, which dissolves cement paste in the shaft and cone. Plastic chambers do not corrode this way; concrete chambers in septic zones need linings or coatings. Pumping stations are covered in our guide to sewage and wastewater pumps.

Covers and frames: EN 124

EN 124-1:2015, which superseded EN 124:1994, sets definitions, classes, design principles, performance requirements and test methods for gully tops and manhole tops with a clear opening up to and including 1,000 mm. It applies together with a material part:

• EN 124-2: cast iron
• EN 124-3: steel or aluminium alloys
• EN 124-4: steel reinforced concrete
• EN 124-5: composite materials
• EN 124-6: polypropylene, polyethylene or PVC-U

The Gulf states publish it as GSO EN 124-1:2021, with the same title and scope. A manhole top is the frame plus cover and/or grating. The clear opening is the diameter of the largest circle that fits in the frame's clear area: the inner diameter of a round frame, the inner side of a square one.

Cover makers advise choosing the heavier class when in doubt.

What the class number means

The number is the test load in kilonewtons the top must carry in a laboratory test; EN 124-1 uses two-thirds of it for the permanent-set check. 250 kN is about 25.5 tonnes-force, hence "25 tonnes", but service loads are far below the test load. The class says where a top may go, not what vehicle may cross it.

Worked example: choosing classes along one street.

• Footway inspection chamber covers: group 2, B125 minimum
• Road gully grating in the kerbside channel, extending 0.4 m from the kerb edge into the road: inside the 0.5 m zone, group 3, C250 minimum
• Sewer manhole in the traffic lane, 1.5 m from the kerb: carriageway, group 4, D400 minimum
• Lorry yard at a depot: parking for all road vehicles, D400 minimum; E600 (group 5) where container handlers or heavy forklifts impose high wheel loads

The D400 test load is 400 kN (about 40.8 tonnes-force), and its permanent-set check is made at 2/3 × 400 = 266.7 kN.

Seating and security

• Stability: in groups 4 to 6, covers must not rock, or must be quiet in use; makers use machined seats, elastomer inserts or three-point suspension
• Securing: EN 124-1 recognises securing features, mass per unit area and locking accessories, and tests how well the cover is held in its frame
• Marking and certification: ask for the standard and class marked on every cover and for third-party certification; an unmarked cover's class cannot be checked on site

Cover materials

Iron covers attract scrap theft; composites and locking covers deter it.

Round, square, grated and sealed

Round covers cannot fall in. A circle has the same width in every direction, so a cover larger than its opening has no orientation that passes through. A square cover can: tilted on edge and turned to the diagonal, it meets an opening √2 times wider than its side. A 600 × 600 mm opening has a diagonal of 849 mm, so a 650 mm cover turned that way has about 200 mm to spare. Square and rectangular covers suit paving and give full access to valve and cable chambers, but on entry shafts they should be hinged or captive.

Other options:

• Gratings admit surface water at gully tops; check slot size and orientation for pedestrians and cyclists against EN 124 and local rules
• Ventilated covers let air in and out, for sewer ventilation or air valve chambers on water mains
• Sealed covers keep odour in and surface water out; bolted covers hold down where a surcharging sewer could lift them
• Recessed tray covers take block paving or concrete to match the surface
• Hinged and lift-assisted covers suit chambers opened often

HDPE and other plastic manholes

Plastic manholes are moulded PE or PP chambers with integral bases, or are fabricated from large-diameter HDPE pipe with welded bases and benching; riser sections set the height. Small units are placed without a crane, welded or sealed joints keep infiltration out, and the plastic does not corrode in septic sewers. Four checks decide whether one works:

1. Product standard and depth: EN 13598-2 for traffic areas, with the maker's limits on depth and groundwater
2. Traffic load path: an HDPE riser alone is normally not adequate for vehicle loads. A rigid concrete cap or support ring, centred over the shaft, carries the cover's load into the ground; makers stress that there should be no load exchange between the cover or ring and the shaft
3. Buoyancy: an empty chamber in groundwater is a float
4. Backfill: granular embedment, compacted in thin lifts with light equipment; one maker asks for at least about 1.07 m (3.5 ft) of compacted embedment around the riser, in lifts of no more than about 200 mm (8 in). Where fine native soil could migrate into it, separate the two with a geotextile

Worked example: buoyancy of an HDPE manhole

A DN1000 PE manhole has a shaft outside diameter of 1.10 m (from the maker's drawing) and a mass of 300 kg. Its base is 4.0 m below ground and the design groundwater level 1.0 m below ground, so 3.0 m is submerged. The worst case is an empty chamber with sealed connections. Assumed unit weights: water 9.81 kN/m³; soil 18 kN/m³ above the water table and 20 kN/m³ saturated (10.19 submerged); concrete 24 kN/m³ (14.19 submerged). Side friction is ignored.

1. Uplift: 9.81 × π/4 × 1.10² × 3.0 = 9.81 × 0.950 × 3.0 = 28.0 kN
2. Chamber alone: 300 × 9.81 = 2.9 kN, about a tenth of the uplift. It floats.
3. Add a concrete ring cast around the base, 1.70 m outside diameter and 0.30 m deep. Ring volume: π/4 × (1.70² − 1.10²) × 0.30 = 0.396 m³, giving 0.396 × 14.19 = 5.6 kN submerged. Soil over the ring: 1.32 m² × (1.0 × 18 + 2.7 × 10.19) = 1.32 × 45.5 = 60.1 kN. Total stabilising weight: 2.9 + 5.6 + 60.1 = 68.6 kN
4. Uplift check: EN 1997-1 treats this as the UPL limit state and factors the actions; one national annex, for example, applies 1.0 to destabilising and 0.9 to stabilising permanent actions. 0.9 × 68.6 = 61.7 kN against 1.0 × 28.0 = 28.0 kN: it passes, with a ratio of 2.2
5. Construction stage: with backfill only 1.2 m above the ring and the excavation flooded to the design groundwater level, the soil gives 1.32 × 1.2 × 10.19 = 16.1 kN. Then 0.9 × (2.9 + 5.6 + 16.1) = 22.1 kN, less than 28.0 kN: it fails. About 1.7 m of compacted backfill over the ring is needed before the water can return, on this method (submerged weights, factors 1.0 and 0.9). Factoring the water pressure on the whole base against total weights, or using 1.1 on destabilising actions, raises it to about 1.9–2.3 m.

What the example shows. About 88% of the resistance is the soil the ring engages, not the concrete, so the ring must be locked to the chamber and the backfill compacted. Construction is the dangerous stage, which is why one maker's installation guide calls for dewatering until backfilling is complete. Use your own national annex and the maker's data.

Installing frames and covers

• Base: a sound, level precast cover or reducing slab, brought to level with purpose-made adjustment units, not loose bricks, tiles or packers that leave voids
• Bedding: a full bed of purpose-made mortar (rapid-setting where traffic returns quickly), carried over the frame flange, with no voids under the seating
• Level: flush with the surface and to its crossfall; a proud or sunken frame takes an impact from every wheel
• Plastic chambers: the concrete ring sits centrally over the shaft without bearing on it
• Concrete pavements: plan the joints around frames so slab cracks do not run into them; joint load transfer is covered in our dowel bars guide
• Curing: keep traffic off until the bedding mortar reaches the strength its maker specifies

Manholes also take the outflow of subsurface drainage layers; see our guide to geocomposites.

Common Mistakes

1. Specifying C250 for a manhole in the carriageway. EN 124 defines C250 for gully tops in the kerbside channel zone, not the running lanes, where under-rated covers rock loose or break.

   Prevention: Take the class from the EN 124 installation group: D400 minimum in carriageways, hard shoulders and parking areas for all vehicles.

2. Reading the class as a vehicle rating. "40 tonnes" is a laboratory test load, not an axle or vehicle limit.

   Prevention: Select by location group, and choose the higher class when in doubt.

3. Fitting a loose square cover to an entry shaft. It can drop through its own opening onto someone below.

   Prevention: Use round covers on entry shafts, or hinged or captive square covers.

4. Putting a plastic cover where C250 or higher is needed. PP, PE and PVC-U tops to EN 124-6 are limited to A15 and B125.

   Prevention: Use ductile iron, steel or composite tops of the required class in kerbside channels, carriageways, hard shoulders, lorry parks and other group 3 to 6 locations.

5. Ordering a DN600 chamber for personnel entry. EN 476 sets 1,000 mm, or 800 mm exceptionally.

   Prevention: State whether entry is needed and size the chamber to EN 476 or the national rule.

6. Skipping the buoyancy check, or stopping dewatering early. An empty plastic chamber lifts when groundwater returns before backfilling is complete.

   Prevention: Check uplift at the design groundwater level and at the construction stage, and keep dewatering until the backfill is in.

7. Seating the frame on a plastic shaft or loose packing. Wheel loads distort the shaft, or the frame rocks and breaks out.

   Prevention: Carry the frame on a concrete ring or slab, on a full mortar bed.

Ordering checklist

• Network: foul, surface water or combined; pipe sizes and materials; number and angles of connections; depth to invert
• Ground and traffic: groundwater level for design and during construction, soil type, traffic at each cover
• Chamber: manhole or inspection chamber; internal size and shape; material and product standard; riser sections; steps or ladder; benching
• Cover and frame: clear opening, shape, EN 124 class for each location, material, solid, grating, ventilated or sealed, locking or hinged, frame depth, surface finish
• Plastic chambers: chamber mass and outside dimensions for the buoyancy check, base flange or ring detail, maximum depth, load-distribution ring detail
• Documents: EN 124 certification and marking, data sheets, test certificates
• Quantities: number of each chamber and cover type by class

Supply from Kasko Makine

Kasko Makine supplies manholes and manhole covers for drain and sewer systems:

• Kasko Mak branded manholes: polyethylene (HDPE) manholes for drainage and sewer systems, for inspection, access and system control, in DN600, DN800, DN1000 and custom diameters, with adjustable riser sections. Covers are rated C250 as standard and D400 for heavy duty (the EN 124 class applies to the frame and cover, carried on a concrete ring, not to the PE chamber). The page states that each manhole is load-tested and dimensionally verified before dispatch, and that product data sheets and compliance certificates come with every order
• Manholes: manholes for drain and sewer systems, supplied with C250 covers as standard and D400 versions available
• Square manholes, square manholes with holes (holes for drainage, ventilation or service access), square easy-access manholes (for convenient inspection and personnel access) and grille manholes (grille covers for drainage, inspection and access): each rated C250 as standard, with D400 versions available
• Special manholes: for customised applications and project requirements, C250 as standard with D400 available

Engineering support: Send the drainage layout or manhole schedule with depths, pipe connections, groundwater level and the location of each cover. We will review chamber sizes and cover classes against your data and quote chambers, covers and frames together.

Send your manhole schedule with depths, groundwater level and cover locations for a quotation — we reply within 24 hours. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading

• HDPE Pipes: Properties, Grades and Specifications
• Geocomposites: Drainage Types, Testing, Design and Applications
• Sewage and Wastewater Pumps: Types, Impellers and Selection
• Wastewater Treatment Equipment: Screens, Clarifiers, Aeration and Dewatering
• Air Release Valves for Water Pipelines: Types, Placement and Sizing

Frequently Asked Questions

Q: What is the difference between a manhole and an inspection chamber?
A: Under EN 476, a manhole is a chamber with a removable cover on a drain or sewer that permits entry by personnel. An inspection chamber also has a removable cover but only admits cleaning and inspection equipment from the surface, not people. Where no national rules apply, a circular manhole needs at least 1,000 mm internal diameter, so a DN600 chamber is an inspection chamber.

Q: What are the EN 124 load classes for manhole covers?
A: EN 124-1 has six classes named by test load in kilonewtons: A15 for pedestrian and cycle areas, B125 for footways and car parks, C250 for gully tops in kerbside channels, D400 for carriageways, hard shoulders and parking areas for all vehicles, E600 for high wheel loads such as docks, and F900 for particularly high wheel loads such as aircraft pavements.

Q: Where can a C250 manhole cover be used?
A: Where EN 124-1 asks for A15 or B125, such as footways, pedestrian areas and car parks, a C250 cover exceeds the minimum. C250 is the minimum only for gully tops in the kerbside channel, within 0.5 m into the carriageway and 0.2 m into the footway. Manhole covers anywhere in the carriageway, including that kerbside strip, on hard shoulders or in parking areas for all vehicles need D400 at least. The 25 tonnes often quoted is a test load.

Q: Why are most manhole covers round?
A: A round cover has the same width in every direction, so it cannot fall through its own opening however it is turned. A square cover can drop through along the diagonal, which is about 1.41 times its side. Round covers also need no alignment when they are replaced. Square covers are used for paving and rectangular chambers, preferably hinged or captive on entry shafts.

Q: What is the minimum size of a manhole?
A: Where no national rules apply, EN 476 sets minimum internal dimensions for manholes of 1,000 mm diameter for circular chambers, 750 by 1,200 mm for rectangular, 1,000 by 1,000 mm for square and 900 by 1,100 mm for elliptical. A circular minimum of 800 mm is allowed in exceptional circumstances. The cover's clear opening should be at least 600 mm.

Q: How do you stop an HDPE manhole from floating?
A: Compare the uplift, the weight of water displaced by the empty chamber below the water table, with the stabilising weight of the chamber, any concrete ring and the soil the ring or base flange engages, applying the partial factors of your national annex to EN 1997-1. Keep the excavation dewatered until backfilling is complete; the construction stage is often critical.

Q: Which material is best for manhole covers?
A: Ductile iron is the usual choice for roads because it is tough and light for its class. Grey iron is brittle and mainly used for like-for-like replacement. Steel suits fabricated sizes and recessed paving trays, composites suit theft-prone areas and electrical chambers, and PP, PE or PVC-U covers are limited to classes A15 and B125. Choose the class first, then the material.